The present invention relates to a method that greatly simplifies the fabrication of superconductor coated substrates by directly depositing a biaxially aligned superconductor onto a nonbiaxially aligned substrate.
These inventions relate to improved technology for making so-called xe2x80x9csecond generationxe2x80x9d second generation high temperature superconductors. Research efforts around the world have shifted away from the powder in tube (BSCCO) technology to development of YBCO coated conductors. The reason for this shift is because YBCO superconductors possess greatly enhanced critical current densities while at the same time exhibiting lower degradation in the presence of external magnetic fields.
Other researchers have found that enhancement of JC can be obtained by selectively doping the grain boundaries of YBCO superconductors with calcium. These investigators fabricated multilayer structures of YBCO and YBCO with calcium on SrTiO3 bicrystals with [001] tilt angle of 24 degrees (i.e. the misorientation angle). The result showed that the Ca-doped YBCO grain boundaries can have a very high JC even if the grain boundary misorientation angle is as great as 24 degrees, see xe2x80x9cEnhanced Supercurrent Density in Polycrystalline High TC Superconductors at 77Kxe2x80x9d by G. Hammerl et al. that appeared in the Sep. 12, 2000 issue of Journal Nature.
Most current research efforts are focused on using nickel or nickel alloys as a flexible substrate. These substrates, however, must first be coated with cerium oxide. The layering is necessary to provide the desired lattice matching and to prevent diffusion of the nickel from the substrate into the biaxially textured superconducting layer. One method being utilized to fabricate these textured substrates is the RABiTS (Rolling Assisted Biaxially Textured Substrate) process developed at Oak Ridge National Laboratory. IBAD (ion-Beam Assisted Deposition) developed at Los Alamos National Laboratory, and ISD (Inclined Substrate Deposition) developed at Argonne National Laboratory are processes used to deposit a biaxially textured oxide layer on an untextured substrate. The essential step in each of these methods is fabrication of a textured substrate, i.e., a substrate whose individual grains are extremely well aligned in two orthogonal directions. On top of the textured substrate, before YBCO can be deposited, other non-superconducting layers must be grown to provide a better match with YBCO properties such as lattice spacing and thermal expansion and to minimize reaction between YBCO and the substrate. Deposition of each layer requires precise control of the process, increases the time and cost associated with fabrication of the conductor, and increases the chance that flaws will develop.
Various methods heretofore described, the RABiTS, IBAD and ISD methods of forming second generation high temperature superconductors, all have draw backs, mostly related to the number of layers which need to be deposited and the associated amount of time necessary to produce them. What is needed is a method of producing second generation superconductors which can use the speed inherent in the ISD method without the need to form intermediate layers.
Accordingly, it is an object of the present invention to provide a method for rapidly producing second generation superconductors in which a biaxially aligned superconductor layer is directly deposited on a non-biaxially textured substrate which is compatible with the superconductor and substantially chemically inert with respect thereto. It is preferred that atoms of the substrate do not migrate into the superconductor.
Another object of the invention is to provide a method for directly depositing a biaxially aligned superconductor on a substrate which may be untextured or axially textured.
Yet another object of the present invention is to establish a plume of superconductor material and directly deposit the superconductor material on an untextured metal substrate using the ISD method, wherein the metal substrate is chemically substantially inert to the superconductor.
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.